The invention relates to an automatic adjustment device for a mechanically actuated disk brake, including a sliding saddle that moves on a diagonal relative to the brake disk and whose two saddle halves, each has a brake lining support and a brake lining, cover the brake disk, an actuating shaft that has a rotating mount in one of the saddle halves, the bushed end of which exhibits a radially projecting collar, one side of which is furnished with diagonal tracks for the reception of balls, which tracks correspond to diagonal tracks on a bearing ring and serve to convert the rotational motion of the actuating shaft into the axial motion of a pressure screw which is mounted in torque-resistant fashion to a piston, while the actuating shaft is supported by an axial bearing on the sliding saddle to secure it against axial displacement on the side of the collar facing away from the diagonal tracks, and the bearing ring is capable of axial motion relative to the brake saddle, but is secured against rotation, and is supported by a sleeve-like adjustment nut into which the pressure screw is screwed and which is attached in torque-resistant fashion to an extension piece which coaxially passes through the actuating shaft. An adjustment ring is rotationally mounted relative to the extension piece, the adjustment ring or the actuating shaft having a radial pin that engages in a groove of the actuating shaft or of the adjustment ring. An adjustment sleeve is positioned on the extension piece, the adjustment ring and the adjustment sleeve having spiral gearings on their facing sides, and one of the two adjustment parts having a spiral gearing supported by a collar of the adjustment nut. A spring component is supported on the other adjustment part in order to maintain the engagement of the two spiral gearings, a directional clutch is positioned in the power flow from the adjustment ring to the adjustment nut and takes effect in the direction of brake actuation upon rotation of the actuating shaft, and a torque limiting device limits the torque that can be transferred from the adjustment ring to the adjustment nut.
An adjustment device of this type described in German Patent Document DE-OS 38 14 475 employs a movable saw-tooth catch to adjust the wear on brake linings by stages. The clearing play is thus determined by the selected tooth spacing. Reducing the clearing play with a very small spacing is impossible for manufacturing reasons, however.
Thus in overcoming the clearing play, a correspondingly large actuation stroke (return stroke) is necessary for brake actuation, and a reduction in the actuation path reserve may also be evident. The size of the actuating stroke, however, is also determined by the incline of the diagonal tracks on the bearing ring and on the actuating shaft. A small incline demands a relatively large actuating stroke to provide the necessary spread. An increase in the incline, which results in a more rapid positioning of the brake shoe on the brake disk when the actuating stroke is reduced, requires larger actuating cylinders to achieve the same braking effect, due to reduced transmission.
In actual practice the object is to reduce the actuation stroke by means of a minimal return stroke and a clearing play that approaches zero, in order to thereby achieve a more rapid contact of the brake shoe with the brake disk and ultimately to increase the actuation reserve for emergency and complete braking. This requirement is primarily an objective when disk brakes of the given type are to be effectively employed in ABS (antilocking system) braking apparatus, i.e. reduced air consumption per braking action, faster filling times for the actuation cylinders, and thus shorter pressure buildup times for the overall brake apparatus. Given an equal total transmission for the actuating mechanism, faster brake lining contact is achieved due to shorter return strokes.
This requirement can only be fulfilled by a continuously adjustable regulating device, which also operates in a force-dependent manner. In addition, the inventive adjustment device must provide a noticeable simplification vis-a-vis the state of the art, with a reduction of the number of necessary adjustment parts. The adjustment device of the invention must also make possible a simpler reset procedure, while both eliminating chatter upon rapid skipping of the spiral gearing and avoiding the use of a clearance ring for the frictional connection, inasmuch as such rings make resetting more difficult due to fluctuations in the frictional value.